1. Field of the Invention
Embodiments of the present invention generally relate to a gripping apparatus for supporting tubulars. Particularly, the aspects of the present invention relate to slip type gripping assembly disposable within a rotary table.
2. Description of the Related Art
The handling of pipe strings has traditionally been performed with the aid of a spider. Typically, spiders include a plurality of slips circumferentially surrounding the exterior of the pipe string. The slips are housed in what is commonly referred to as a “bowl”. The bowl is regarded to be the surfaces on the inner bore of the spider. The inner sides of the slips usually carry teeth formed on hard metal dies for engaging the pipe string. The exterior surface of the slips and the interior surface of the bowl have opposing engaging surfaces which are inclined and downwardly converging. The inclined surfaces allow the slip to move vertically and radially relative to the bowl. In effect, the inclined surfaces serve as a camming surfaces for engaging the slip with the pipe. Thus, when the weight of the pipe is transferred to the slips, the slips will move downwardly with respect to the bowl. As the slips move downward along the inclined surfaces, the inclined surfaces urge the slips to move radially inward to engage the pipe. In this respect, this feature of the spider is referred to as “self tightening.” Further, the slips are designed to prohibit release of the pipe string until the pipe load is supported by another means.
In the makeup or breakup of pipe strings, the spider is typically used for securing the pipe string in the wellbore. Additionally, an elevator suspended from a rig hook is used in tandem with the spider. The elevator may include a self-tightening feature similar to the one in the spider. In operation, the spider remains stationary while securing the pipe string in the wellbore. The elevator positions a pipe section above the pipe string for connection. After completing the connection, the elevator pulls up on the pipe string to release the pipe string from the slips of the spider. Freed from the spider, the elevator may now lower the pipe string into the wellbore. Before the pipe string is released from the elevator, the spider is allowed to engage the pipe string again to support the pipe string. After the load of the pipe string is switched back to the spider, the elevator may release the pipe string and continue the makeup process.
Traditionally, a spider is located above a rotary table situated in the rig floor. More recently, flush mounted spiders have been developed so that the spider does not intrude upon the work deck above the rotary. Because flush mounted spiders reside within the rotary table, the pipe size handling capacity of the spider is limited by the size of the rotary table. Current spider designs further augment the problem of limited pipe size handling capacity. Thus, in order to handle a larger pipe size, a larger rotary table must be used. However, the process of replacing the existing rotary table is generally economically impractical.
Another drawback of some spiders currently in use is the guide plate for facilitating the axial movement of the pipe string. The guide plate is typically designed for use with a certain pipe diameter size. Therefore, the guide plate must be replaced when a different pipe size is used. Further, many spiders have slips that are held in position in the bowl by friction. As a result, only a limited amount of torque may be applied before slippage occurs between the slip and the bowl.
There is a need, therefore, for a gripping apparatus with increased pipe size handling capacity. There is a further need for a gripping apparatus having a guide plate capable of accommodating one or more pipe size. There is a further need for a gripping apparatus with increased torque capacity.